After reading Xenopus’ masterly explanation of how cyanide and nerve gasses do their dastardly work, I was reminded of Annie Dillard’s Pilgrim at Tinker Creek. I recall her stating that if you replace the iron atom at the center of a hemoglobin molecule with another element (phosphorus?), you suddenly have chlorophyll. So, my questions are:
*are these two chemicals really identical except for that one single element?
*what is that one element if I’m not mistaken?
*I know that chorophyll is integral to photosynthesis, and the whole plant cycle thing, but do these two molecules play analogous roles among animals and plants?
*and if so, how do peaches manage to reproduce when they have all that cyanide in the pit? Wouldn’t it attack the chlorophyll in a similar fashion to hemoglobin?
I don’t really know the structure of chlorophyll, but I don’t think it is a quaternary structure of proteins like hemoglobin is. When learning about the quaternary structure of proteins, hemoglobin is always mentioned, chlorophyll is never mentioned.
Chlorophyll’s job is to absorb light in and use that light for energy. Hemoglobin, OTOH, transfers oxygen around the body via circulation. Because of this, hemoglobin and chlorophyll do not have analogous roles in plants and animals.
The two chemicals are not identical except for the single element. Both do, however, contain a similar porphyrin ring system that bears a central metal atom (iron for hemoglobin and magnesium for chrorophyll.) There also are different proteins associated with the two molecules. They are really quite similar though, given their very different roles.
As TheUnforgiven states, they do not play analogous roles in plant and animals.
Cyanide binds very tightly to hemoglobin (displacing oxygen) because the iron atom can form two additional bonds beyond the four that are involved in its normal attachment to the porphyrin ring. Magnesium can not bond like this. So, my somewhat educated guess is that chlorophyll is not disturbed much by cyanide.
Just echoing what OrganicMatter alreasy said (drat! :)), with an excerpt from my chem book:
"The principal ligand (a molecule or anion that can bind to a metal ion to form a complex) structure in many biologically active complexes is due to the square planar (a molecule with a central atom having four bonds that point to the corners of a square) arrangement of nitrogen atoms in a polydentate ligand structure (a ligand that has two or more atoms that can become simultaneously attached to a metal ion) called the “porphyrin structure”.
Related ligand structures are found in hemoglobin, and myglobin which contain a porphyrin ligand that holds iron. These bind oxygen as an additional ligand attached to the iron ion. Chlorophyll contains a similar ligand structure in which magnesium is held."
Information in parentheses are to help those who don’t know the meanings of the terms.
